This invention relates to measurement of angular or linear displacements and especially to measuring the angular displacement caused by spline wear of two shafts coupled by a spline in a slot.
Many rotating machines consist of a driver unit and a driven machine, the shafts of the two being coupled fixedly to each other by means of a spline on one shaft which fits into a slot in the other shaft. The slot and spline wear away with continued use and it is desirable to have a means for measuring such wear while the machines are in use.
A previous method of wear measurement employed the generation of timing pulses by magnetic pickups (monopole generators) and the use of a standard digital time-interval meter to measure the change in the time interval between the pulses as coupling wear progressed. This method, which is illustrated in FIG. 1, proved to be unsatisfactory when applied to spline wear test due to torsional oscillation and other mechanical disturbances (of amplitudes greater than the signal to be measured) which disrupted the time interval meter operation. Torsional oscillations, for example, induced a rapid change in the time interval which caused random variations in the time interval meter. Averaging techniques had to be applied to the meter readings to establish the true time-interval change and this averaged value was then used to manually calculate coupling wear from an equation.
The average values proved to be more accurate than the raw data, but were not of sufficient accuracy for some types of research data application. Standard time interval measurement equipment has also proved to be subject to errors induced in triggering from the unbuffered magnetic pickup signals, since signal amplitudes also vary significantly due to torsional and linear oscillations inherent in most rotating machinery.
Accordingly, it would be very desirable to develop a method of measuring the oscillating time interval between pulses of varying amplitudes and of averaging or cancelling out the periodic oscillations due to torsional or linear vibration, since no suitable instrumentation now exists. The developed instrumentation method has to be compatible with standard digital and analog recording and display devices. In summary, the disadvantages of existing methods of measuring angular or linear displacements are:
a. Static measurements require stopping the machinery, thereby suspending any tests in progress.
b. A Time Interval Meter approach permits dynamic measurements to be made but is unstable and inaccurate when torsional or linear oscillations disturb the timing signals.
c. A Time Interval Meter approach does not readily permit automatic recording and display of coupling displacement in direct engineering units.
d. A Time Interval Meter approach does not readily permit automatic monitoring and shutdown of machinery upon attaining a preset angular or linear displacement threshold.
e. Existing methods provide no direct display or recording of displacements in engineering units.